EGT Thermocouple Circuit Design Tips

[Fred]

EGT sensors require a conditioning circuit, which can be made from discretes, but is best done with a dedicated IC such as those from Analog Devices. The following two documents contain notes on getting the most out of them.

http://www.analog.com/static/imported-f ... AN-274.pdf
http://www.analog.com/static/imported-f ... AN-369.pdf

The AD595 and friends have been replaced with the AD8495 and friends. http://www.analog.com/en/mems-sensors/a ... oduct.html

The supply voltage for these chips is raw 12V because they can handle up to 36V and because the supply doesn't affect the reading, just the range. IE, when your alternator is charging you can hit higher temperatures than when it's not. Having said that, the new device has twice the range of the old one so can hit 1000C on 5V. Thus feeding it 9V or even lower from a tiny smd regulator might be a good idea for consistency sake. On the output you just scale the voltage to 5V from your expected max with a divider and cap it with schottkys in case of a nuclear melt down in the engine bay.

These come in a SOIC8 suitable for a small project like our favourite and currently anonymous one by Dan.

Fred.

[Dan]

anonymous? LOL

I like them. Skype tonight (my time) if you are free?

[Fred]

Yep, sounds good! :-)

[tpsretard]

i would recommend 8 Volts.
Way to busy to do the research for you.
However All systems i work with went to 8Volts a LONG time now. Motec, pectel, Life racing, Tag...etc...etc...

All use 8v on egt drivers and can and a bunch of other things.
Said it is the highest they could go without problems if the charging system stops..

[Fred]

Yep, I'd agree with that, however the correct/desirable voltage is completely dependent on the IC in use, and they all vary. So as a general recommendation, it's completely meaningless. In the case of this IC, 5V gives up to 1000C, which is usually enough. 8V would give 1600C at which point your engine is a puddle of metal on the road :-)

[johntramp]

Is a digital IC a better option then?
http://www.maxim-ic.com/datasheet/index.mvp/id/7273

[Fred]

Not necessary 1000C = 1832 °F = well above normal anyway.

[tpsretard]

with the ALS and EGR on in the Group B car we have logged 1320deg :S

[Fred]

Fair enough! :-)

[Fred]

Wait, F or C ?